An explosive device detonated inside a garbage can near a charity racecourse in Seaside Park, New Jersey, on Sept. 17, 2016.

WASHINGTON (AP) — Three explosives devices found Saturday in New York and New Jersey used the same kind of flip cellphone as a trigger and were made with commonly available materials that can be bought without raising law-enforcement suspicions.

A federal law enforcement official said investigators found evidence of a pressure cooker, flip cellphone, small pieces of steel and residue from the explosive compound Tannerite in the remnants of bomb that exploded under a dumpster and wounded 29 people Saturday night in New York City. A second pressure cooker bomb with a similar cellphone with wires exposed was found nearby and safely removed by authorities.

Hours before the New York blast, a pipe bomb constructed from a threaded pipe fitted with end caps exploded in a garbage can in a New Jersey shore town. The official said that bomb also used a flip cellphone, along with a strand of Christmas lights likely used to complete an electric circuit that ignited black powder found in the device.

The official was not authorized to publicly discuss details of the ongoing investigation and spoke on condition of anonymity.

Ahmad Khan Rahami, a 28-year-old naturalized citizen originally from Afghanistan, was arrested in connection with the bombings Monday after a shootout with police in Linden, New Jersey, which lies about 24 miles southwest of New York City.

Nearly every piece of the bombs recovered is readily available at sporting goods stores, corner convenience stores or on the internet. The instructions for building them is a mere Google search away.

Using pressure cookers to house bombs was popularized years ago by Inspire magazine, an English-language online publication produced by an al-Qaida affiliate and used by the brothers who bombed the Boston Marathon in 2013.

But while pressure cookers are advocated by terrorist organizations, their use does not necessarily suggest that someone received specialized training or was under the control of a foreign group

“It’s not that difficult to go on the internet, find out what explosive compounds are out there, where they’re available – either through internet order or retail stores” and then create them on your own, said John Cohen, a top former counterterrorism official at the Department of Homeland Security.

The fact that different materials were found in different explosives suggests that the suspected bomber likely acquired the materials online or simply used whatever was readily available, he said.

It’s not uncommon for radicalized extremists to acquire online the knowledge needed to carry out an attack in whatever form.

“Others who have gone through that same path get a gun, others use a knife,” Cohen said. “This guy, as the Boston Marathon bombers did, decided to build explosive devices.”

Federal law enforcement has been concerned about the growing popularity of Tannerite and other compounds used for exploding firearms targets in recent years.

Charles Mulham, a retired special agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives, said when the exploding targets were first developed, he was worried about the easy availability of the compounds.

“I saw this product come out and thought, oh my God, it’s just a matter of time before someone takes this and uses it for nefarious purposes,” Mulham said.

In recent years there have been multiple reports of injuries related to explosions of the compounds. Those explosions are usually ignited by a high-velocity shot from a rifle.

The compounds are routinely sold in two parts, including an oxidizer such as ammonium nitrate and aluminum or another metal-based powder that become explosive when combined. The compounds are not regulated by the ATF because they are sold separately. Anyone using the products doesn’t need an explosives license unless they are transporting the combined compounds or using them commercially.

The ATF has issued multiple advisories about the products and their use, and has warned that once combined, the compounds are a “high explosive,” which detonate quickly and can cause a powerful blast.